[PATCH 3/5] btrfs: use add_old_bytes when updating global reserve

[Josef Bacik <josef@toxicpanda.com>]

We have some annoying xfstests tests that will create a very small fs,
fill it up, delete it, and repeat to make sure everything works right.
This trips btrfs up sometimes because we may commit a transaction to
free space, but most of the free metadata space was being reserved by
the global reserve.  So we commit and update the global reserve, but the
space is simply added to bytes_may_use directly, instead of trying to
add it to existing tickets.  This results in ENOSPC when we really did
have space.  Fix this by returning the space via
btrfs_space_info_add_old_bytes.  The global reserve _can_ be using
overcommitted space, but the add_old_bytes checks this and won't add the
reservation if we're still overcommitted, so we are safe in this regard.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/block-rsv.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/block-rsv.c b/fs/btrfs/block-rsv.c
index 18a0af20ee5a..394b8fff3a4b 100644
--- a/fs/btrfs/block-rsv.c
+++ b/fs/btrfs/block-rsv.c
@@ -258,6 +258,7 @@ void btrfs_update_global_block_rsv(struct btrfs_fs_info *fs_info)
 	struct btrfs_block_rsv *block_rsv = &fs_info->global_block_rsv;
 	struct btrfs_space_info *sinfo = block_rsv->space_info;
 	u64 num_bytes;
+	u64 to_free = 0;
 	unsigned min_items;
 
 	/*
@@ -300,9 +301,7 @@ void btrfs_update_global_block_rsv(struct btrfs_fs_info *fs_info)
 		btrfs_space_info_update_bytes_may_use(fs_info, sinfo,
 						      num_bytes);
 	} else if (block_rsv->reserved > block_rsv->size) {
-		num_bytes = block_rsv->reserved - block_rsv->size;
-		btrfs_space_info_update_bytes_may_use(fs_info, sinfo,
-						      -num_bytes);
+		to_free = block_rsv->reserved - block_rsv->size;
 		block_rsv->reserved = block_rsv->size;
 	}
 
@@ -313,6 +312,9 @@ void btrfs_update_global_block_rsv(struct btrfs_fs_info *fs_info)
 
 	spin_unlock(&block_rsv->lock);
 	spin_unlock(&sinfo->lock);
+
+	if (to_free)
+		btrfs_space_info_add_old_bytes(fs_info, sinfo, to_free);
 }
 
 void btrfs_init_global_block_rsv(struct btrfs_fs_info *fs_info)
-- 
2.21.0